First surprise is that you get revenue of around 59BTC in your "three small Stores" and then this much revenue might be so insignificant to you that you didn't even notice them, This means you must be having revenue of at least 10 million or more, anyways, not my business. But for sure you must immediately sue these criminals, you must be having invoices of all the customers that have used the POS, this means you will be able to reconcile the inputs in the address, and similarly reconcile the outputs with some other sort of withdrawals that you might have done. Complain the police that the balance doesn't reconcile and file a complain against the POS terminal company.
The $3 million price he quoted was the value today. Depending on the times the transactions were made, it could be less then $150000.
Which is still a significant amount, but depending on the circumstances not unbelievable.
If these machines were getting a lot of use in a major city scraping some money off the top would not be impossible. Depending on how the machines were setup and used.
Lets face it, if the ATM operator is just renting space and giving the OP a cut of the profits then it's not impossible that they were vastly under reporting the amounts.
-Dave